This invention relates to a process and apparatus for shaping metal containers such as aerosol containers; and more particularly, to the manufacture of shaped aerosol containers using air as the pressurization medium.
Aerosol containers or cans are used for a variety of personal grooming and household products including, among other things, products dispensed as a spray, a gel, or a foam. The containers have a main body section usually of a uniform diameter, cylindrical shape, with a dispensing valve assembly attached to the upper end of the body and a dome shaped end piece attached to the lower end of the body. However, it is known to form or shape the container so the profile of the container body has a non-uniform contour. Shaping cans is accomplished in different ways, one of which is to form the can body into a cylindrical shape, place the resulting blank or preform into a mold whose interior surface is formed into the desired final shape, and then inject a pressurized fluid into the can. The force created by the fluid pushes on the sidewall of the can body and forces it against the side of the mold, thereby conforming the can body shape to that of the mold.
In this regard, it is well-known to use compressed air as the pressurizing fluid. For example, U.S. Pat. No. 3,224,239, which issued in 1965, describes placement of a straight sidewall, cylindrical can body (17) into a mold (13). The mold has a cavity (20). A piston (10) is lowered into the container displacing the air in the container so as to compress the air. As a consequence, “The resultant air pressure within the can will be sufficient to cause a plastic flow of the can body 17 to conform with the cavity 20 of the mold 13.” In co-pending, co-assigned U.S. patent application Ser. No. 10/946,593 there is described a dry hydraulic can shaping process in which a bladder is inserted into the can preform once it is in the mold. The bladder is then pressurized with air, or another fluid, which forces it against the sidewall of the can body and forces the sidewall to conform to a shape defined by the mold.
Over the years, a number of other patents have issued which describe various can shaping techniques in which air is the pressurizing fluid. For example, U.S. Pat. Nos. 2,742,873, 3,688,535, 5,187,962, 5,746,080, 5,829,290, 5,832,766, 5,938,389, 5,960,659, 5,970,767, and 6,026,670, describe methods and techniques for making shaped metal cans. In general, these patents describe placement of a preform container in a mold and then using a pressurized fluid to expand the sidewall of the container against the inner surface of the mold so to conform the shape of the container to the shape of the mold. Among the features described in some of these patents are a partial annealing process carried out at elevated temperatures (450°-500° F.) so to partially anneal the cans and increase their ductility, as well as place the preform in a mold which, when it closes, presses against at least a portion of the blank to precompress it before the pressurization process begins.
One issue with the making of shaped aerosol containers is process time and throughput. The present invention is directed to the manufacture of shaped metal cans using pressurized air as the pressurization medium, and in which the throughput of cans is substantially increased over known manufacturing methods.